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- Dewhurst, Richard, et al.
(author)
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It depends on how you look at it: Scanpath comparison in multiple dimensions with MultiMatch, a vector-based approach
- 2012
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In: Behavior Research Methods. - : Springer Science and Business Media LLC. - 1554-3528.
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Journal article (peer-reviewed)abstract
- Eye movement sequences---or scanpaths---vary depending on stimulus characteristics and task (Foulsham \& Underwood, 2008; Land, Mennie, \& Rusted, 1999). Common methods for comparing scanpaths, however, are limited in their ability to capture both the spatial and temporal properties of which a scanpath consists. Here we validate a new method for scanpath comparison based on geometric vectors, which compares scanpaths over multiple dimensions retaining positional and sequential information (Jarodzka, Holmqvist, \& Nyström, 2010). `MultiMatch' was tested in two experiments and pitted against ScanMatch (Cristino, Mathôt, Theeuwes, \& Gilchrist, 2010), the most comprehensive adaptation of the popular Levenshtein method. Experiment 1 used synthetic data, demonstrating the greater sensitivity of MultiMatch to variations in spatial position. In experiment 2 real eye movement recordings were taken from participants viewing sequences of dots, designed to elicit scanpath pairs with commonalities known to be problematic for algorithms (for example, when one scanpath is shifted in locus, or fixations fall either side of an AOI boundary). Results illustrate the advantages of a multidimensional approach, revealing how two scanpath differ. For instance, if one scanpath is the reverse copy of another the difference is in direction but not the position of fixations; or if a scanpath is scaled down, the difference is in the length of saccadic vectors but not overall shape. As well as having enormous potential for any task in which consistency in eye movements is important (e.g. learning), MultiMatch is particularly relevant for "eye movements to nothing" in mental imagery research and embodiment of cognition, where satisfactory scanpath comparison algorithms are lacking.
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- Foulsham, Thomas, et al.
(author)
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Comparing scanpaths during scene encoding and recognition: A multi-dimensional approach
- 2012
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In: Journal of Eye Movement Research. - 1995-8692. ; 5:4:3, s. 1-14
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Journal article (peer-reviewed)abstract
- Abstract in UndeterminedComplex stimuli and tasks elicit particular eye movement sequences. Previous research has focused on comparing between these scanpaths, particularly in memory and imagery research where it has been proposed that observers reproduce their eye movements when recognizing or imagining a stimulus. However, it is not clear whether scanpath similarity is related to memory performance and which particular aspects of the eye movements recur. We therefore compared eye movements in a picture memory task, using a recently proposed comparison method, MultiMatch, which quantifies scanpath similarity across multiple dimensions including shape and fixation duration. Scanpaths were more similar when the same participant's eye movements were compared from two viewings of the same image than between different images or different participants viewing the same image. In addition, fixation durations were similar within a participant and this similarity was associated with memory performance.
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- Foulsham, Tom, et al.
(author)
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Modeling eye movements in visual agnosia with a saliency map approach: Bottom–up guidance or top–down strategy?
- 2011
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In: Neural Networks. - : Elsevier BV. - 1879-2782 .- 0893-6080. ; 24:6, s. 665-677
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Journal article (peer-reviewed)abstract
- Two recent papers (Foulsham, Barton, Kingstone, Dewhurst, & Underwood, 2009; Mannan, Kennard, & Husain, 2009) report that neuropsychological patients with a profound object recognition problem (visual agnosic subjects) show differences from healthy observers in the way their eye movements are controlled when looking at images. The interpretation of these papers is that eye movements can be modeled as the selection of points on a saliency map, and that agnosic subjects show an increased reliance on visual saliency, i.e., brightness and contrast in low-level stimulus features. Here we review this approach and present new data from our own experiments with an agnosic patient that quantifies the relationship between saliency and fixation location. In addition, we consider whether the perceptual difficulties of individual patients might be modeled by selectively weighting the different features involved in a saliency map. Our data indicate that saliency is not always a good predictor of fixation in agnosia: even for our agnosic subject, as for normal observers, the saliency–fixation relationship varied as a function of the task. This means that top–down processes still have a significant effect on the earliest stages of scanning in the setting of visual agnosia, indicating severe limitations for the saliency map model. Top–down, active strategies – which are the hallmark of our human visual system – play a vital role in eye movement control, whether we know what we are looking at or not.
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- Gidlöf, Kerstin, et al.
(author)
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Using eye-tracking to trace a cognitive process: Gaze behavior during decision making in a natural environment
- 2013
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In: Journal of Eye Movement Research. - : University of Bern. - 1995-8692. ; 6:1, s. 3-14
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Journal article (peer-reviewed)abstract
- The visual behaviour of consumers buying (or searching for) products in a supermarket was measured and used to analyse the stages of their decision process. Traditionally metrics used to trace decision-making processes are difficult to use in natural environments that often contain many options and unstructured information. Unlike previous attempts in this direction (i.e. Russo & Leclerc, 1994), our methodology reveals differences between a decision-making task and a search task. In particular the second (evaluation) stage of a decision task contains more re-dwells than the second stage of a comparable search task. This study addresses the growing concern of taking eye movement research from the laboratory into the ‘real-world’, so findings can be better generalised to natural situations.
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